Cylindrical tanks with a structure having an inner tank and an outer tank are being used to store cryogenic liquids such as liquefied natural gas (LNG), liquefied petroleum gas (LPG), and the like. Patent Document 1 discloses a method for constructing a cylindrical tank having a metallic inner tank and an outer tank that is made of precast (PC) concrete.
In the method for constructing a cylindrical tank, PC sidewalls that will form an outer tank are stood from a base portion that is formed of concrete, a roof that has been assembled on the base portion is air-raised, and an outer tank roof is mounted on a top portion of the PC walls. Then, an annular portion is laid on the base portion, and then an inner tank is set up on the annular portion. The inner tank is assembled by welding a plurality of inner tank lateral plates which are carried in from a construction site entrance of the PC walls in a circular shape, and then welding the inner tank lateral plates from a lowermost level to an uppermost level in order. Then, by laying a cold insulation material on the base portion and filling an inner-outer-tank gap with another cold insulation material, a cylindrical tank that has a function of keeping LNG and the like cool is constructed.